Core B's overall mission is to provide hematopathology support to the human and murine modeling projects that comprise this program. It will do so by focusing on the following specific aims: 1. To provide the infrastructure needed to procure, bank, and evaluate human germinal center B-cell lymphoma specimens 2. To develop and apply specific methods for the detection of markers implicated in the molecular classification and pathogenesis of germinal center B-cell lymphomas 3. To construct tissue arrays to enable the study of potential prognostic, diagnostic, or pathogenic markers 4. To assist in the classification of human germinal center B-cell lymphomas and murine models of these tumors, using a uniform set of pathologic criteria 5. To perform cytogenetic analyses to detect and/or validate the presence of specific chromosomal lesions 6.To create and maintain a repository of human DLBCL cell lines and derived materials for use by PPG investigators The Core will interact directly with Projects 1, 2,4, and 5, and will share reagents, methodologies, and results with Project 3. In doing so, it will provide pathology services that are essential to the Program as a whole.